1. Field of the Invention
The present invention relates to an improvement in a coating apparatus which can adjust the clearance between edges or between the edge and a web or object.
2. Description of the Related Art
FIG. 8 is a left side view, partly in section, of a conventional coating apparatus wherein the clearance between two confronting edges is adjustable. FIG. 9 is a partial front view, on a reduced scale, of the coating apparatus shown in FIG. 8. Referring to FIG. 8, a coating apparatus 1 comprises a split head 5 composed of a first head section 2 and a second head section 3 and including a coating liquid supply slit 4 defined between the first and second head sections 2 and 3 and extending in a longitudinal direction (shown by the arrow A in FIG. 9), a pair of edges 6 and 7 arranged on the top of the head 5 in a confronting relationship and cooperating to form an outlet 4a of the slit 4, a longitudinal recess 8 defined between opposing sides (or portions) 3a and 3b of the second head section 3, and a plurality of adjusting means 10 extending between the opposite sides 3a and 3b of the second head section 3. As shown in FIG. 9, the adjusting means are longitudinally arranged at a fixed interval P.
The edges 6 and 7 may be discrete members. In such a case, the edges 6 and 7 are bolted to the first and second head sections 2 and 3.
Each of the adjusting means 10 comprises a bolt 11 threaded into the side 3a of the second head section 3, a nut 12 threaded on the bolt 11, and a locking member 13 for locking the nut 12 against the side 3b of the second head section 3. The bolt 11 has a front thread 11a and a rear thread 11b. The front thread 11a and the rear thread 11b are different in pitch from each other. Thus, the bolts 11 is in the form of a differential screw and enables fine adjustment. When the bolt 11 is rotated, a pulling or compressive force is developed between the front thread 11a of the bolt 11 and the locking member 13. The edge 7 is deformed under these forces so as to adjust a narrow clearance D of the outlet 4a in the order of a few microns to a few hundred microns.
With the coating apparatus 1, a coating liquid is applied from the outlet 4a of the slit 4 onto a web W of paper Ior plastic film, as supplied from a back-up roll B, so as to form a coating layer C. The thickness of the coating layer C in the longitudinal direction depends on a clearance D. Thus, it is imperative to adjust the clearance D of the outlet 4a in the longitudinal direction (shown by the arrow A).
The coating apparatus 1 may perform a post-coating metering method wherein the amount of a coating liquid as applied from the outlet 4a to the web W is measured before the coating layer C is deposited on the web W. In such a case, the clearance D of the outlet 4a should be widened, for example, about 3.0 to 20.0 mm. The thickness of the coating layer C in the longitudinal direction depends on the longitudinal clearance E formed between the web W and the edge 7. To this end, the bolts 11 of the adjusting means 10 are rotated to deform the edge 7 so as to adjust the clearance E between the web W and the edge 7.
The clearance D of the outlet 4a and the clearance E between the web W and the edge 7 vary depending upon not only one condition, but various conditions, for example, how accurately the edge 7 is machined, how firmly the edge 7 is connected to the head 7, and how high the temperature of a coating liquid is. Thus, it is impossible to determine which portions of the apparatus require adjustment. In the prior art coating apparatus, the distance P between adjacent adjusting means 10 and 10 is minimized to enhance the accuracy of adjustment.
Such an arrangement requires a large number of adjusting means 10 arranged along the length of the apparatus. However, some of the adjusting means 10 may be useless if they are mounted to portions where no adjustment is necessary. Adjustment becomes more difficult as the number of adjusting means increases. It is also difficult to adjust portions between adjacent adjusting means 10 and 10.
In order to overcome the foregoing problems, it is an object of the present invention to provide a coating apparatus wherein the location of adjustment can be freely changed in the longitudinal direction of the apparatus.